In the related art, as an optical reflector, those obtained by depositing a thin film of a metal such as aluminum or silver on the front or back surface of a glass substrate having excellent smoothness have been used.
When a thin metal film is deposited onto the surface of a glass substrate, a relatively high reflectance can be obtained. However, when this is used as a reflector plate for solar power generation (solar reflector plate), the plate is inevitably used outdoors. Accordingly, many problems regarding sand resistance, weather resistance, impact resistance, lightening of weight, and the like should be solved.
Regarding those problems, for example, JP 62-57904 B proposes a reflective heat collector plate obtained by providing a reflective metal (aluminum, silver, or the like) deposition film onto the surface of a metal plate (aluminum, stainless steel, or the like), and coating the outer surface of the metal deposition film with a protective film of a transparent inorganic substance (SiO, SiO2, or the like).
Moreover, JP 57-4003 A proposes a reflector including a substrate formed of an appropriate material such as a metal or an alloy like aluminum, a steel plate, or stainless steel, or plastic, a metal reflective film deposited onto the substrate and formed of aluminum, silver, or the like, and a transparent inorganic protective film deposited onto the surface of the metal reflective film and formed of, for example, a vitreous film such as SiO or SiO2.
In addition, JP 57-125901 A proposes a reflector obtained by providing a laminate-like protective layer formed of elements including a coat formed of de-alkalized metal silicate and a resin coat directly stacked and deposited onto the above coat, onto a metal substrate having a reflective surface.
We found that the reflector plates disclosed in JP '904 and JP '003 are excellent in weather resistance since they have a coat containing an inorganic material as a main component. However, if the reflector plates are used as a solar reflector plate frequently positioned in a region where dust flies such as a desert region, the resistance thereof against the flying sand is insufficient.
We also found that since the reflector plate disclosed in JP '901 includes a resin coat as an uppermost surface layer, the sand resistance thereof is very poor.
Accordingly, it could be helpful to provide a solar reflector plate which maintains an excellent reflectance of a reflective layer and has excellent sand resistance and weather resistance.